The broad objective of this research is to make a comprehensive study of uric acid elimination by the avian kidney with emphasis on how the avian kidney handles the potential solubility problems of urate elimination. We have investigated the basic qualitative patterns and quantitative aspects of uric acid excretion as well as a number of specific factors that have been implicated in urate precipitation (electrolytes, pH, renal mucoids). Current and future work during this grant period consists of (1) in vitro studies of urate and cation interactions in the formation of urate colloids and spherical urate precipitates characteristic of bird urine, (2) isolation and characterization of urinary mucoids in bird urine, (3) investigation of the possible function of urinary mucoids as "protective colloids" for maintaining colloidal urates without flocculation, and (4) evaluation of mucoids and urate spheres in urine flow out of the urinary system.